This is troubling, because we still have no good solution for this problem.
Im on similar configuration, except Python2. Same error occurs whenever I send Houdini jobs to Deadline, even if job completes successfully.
Error: TypeError("'NoneType' object is not callable",) in <bound method TxManager.__del__ of <rman_utils.txmanager.core.TxManager object at 0x000000005E708C88>> ignored